1. Clinical Overview
A fixed-dose combination of a typical antipsychotic (phenothiazine derivative) and an anticholinergic agent. Trifluoperazine is a high-potency antipsychotic used to manage psychotic disorders, while Trihexyphenidyl is added to counteract extrapyramidal symptoms (EPS) induced by the antipsychotic. This combination is primarily used in the management of schizophrenia and other psychotic disorders where EPS is a significant concern.
| Onset | Duration | Bioavailability |
|---|---|---|
| Trifluoperazine: Oral: 30-60 minutes for sedative effects; antipsychotic effects may take several days to weeks. Trihexyphenidyl: Oral: Within 60 minutes. | Trifluoperazine: Up to 12-24 hours (allowing for once or twice-daily dosing). Trihexyphenidyl: 6-12 hours. | Trifluoperazine: Approximately 50-60% (oral). Trihexyphenidyl: Well absorbed, but specific percentage not well quantified; estimated >80%. |
2. Mechanism of Action
Trifluoperazine exerts its antipsychotic effect primarily through potent antagonism of postsynaptic dopaminergic D2 receptors in the mesolimbic pathway of the brain. Trihexyphenidyl competitively blocks central muscarinic acetylcholine receptors (M1), correcting the dopamine-acetylcholine imbalance in the nigrostriatal pathway caused by D2 blockade, thereby reducing or preventing extrapyramidal symptoms.
3. Indications & Uses
- Schizophrenia (acute and chronic management)
- Other psychotic disorders with prominent positive symptoms (e.g., delusions, hallucinations)
4. Dosage & Administration
Adult Dosage: Initially: 1 tablet (5mg+2mg) once or twice daily. Usual maintenance: 2-4 tablets daily in divided doses. Maximum antipsychotic dose should not exceed 40mg trifluoperazine per day. The anticholinergic dose is fixed; additional trihexyphenidyl may be needed in some cases.
Administration: Administer orally with or after food to minimize gastric upset. Tablet can be taken with a full glass of water. Do not crush or chew unless advised. Avoid abrupt discontinuation.
5. Side Effects
Common side effects may include:
- Dry mouth
- Blurred vision
- Constipation
- Drowsiness/sedation
- Dizziness
- Orthostatic hypotension
- Urinary hesitancy or retention
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Other CNS Depressants (Alcohol, Opioids, Benzodiazepines) | Additive CNS depression, respiratory depression, sedation | Major |
| Anticholinergics (Atropine, Antihistamines, TCAs) | Additive anticholinergic toxicity (hyperthermia, delirium, ileus) | Major |
| Levodopa, Dopamine Agonists | Mutual antagonism; reduced efficacy of both | Major |
| QT-prolonging drugs (Class IA/III antiarrhythmics, Macrolides, Fluoroquinolones) | Increased risk of torsades de pointes | Major |
| Enzyme Inducers (Phenobarbital, Carbamazepine, Rifampicin) | Reduced plasma levels of both components | Moderate |
| Enzyme Inhibitors (Fluoxetine, Paroxetine, Fluvoxamine - CYP2D6/1A2 inhibitors) | Increased plasma levels of trifluoperazine, risk of toxicity | Moderate |
| Antihypertensives | Potentiated hypotension | Moderate |
| Metoclopramide, Prochlorperazine | Increased risk of EPS | Moderate |
7. Patient Counselling
- DO take exactly as prescribed. Do not increase dose or stop suddenly.
- DO take with food if stomach upset occurs.
- DO report any involuntary movements of face/tongue/jaw immediately.
- DO rise slowly from sitting/lying position to avoid dizziness.
- DO use sugarless gum/candy for dry mouth and maintain oral hygiene.
- DO use sunglasses and sunscreen due to photosensitivity risk.
- DONT consume alcohol or other sedatives.
- DONT drive or operate heavy machinery until you know how the medicine affects you.
- DONT expose yourself to extreme heat (risk of heatstroke).
- DONT take OTC cold, allergy, or sleep aids without consulting doctor (may contain anticholinergics or sedatives).
8. Toxicology & Storage
Overdose: CNS: Deep sedation, coma, seizures, agitation, confusion, delirium. Anticholinergic Toxidrome: Hyperthermia, flushed dry skin, mydriasis (dilated pupils), tachycardia, ileus, urinary retention. Cardiovascular: Hypotension, arrhythmias (QT prolongation, torsades de pointes), cardiac arrest. Extrapyramidal: Severe dystonia, parkinsonism. Respiratory: Depression, apnea.
Storage: Store below 30°C, in a cool, dry place, protected from light and moisture. Keep in the original blister pack or container. Keep out of reach of children and pets. Do not use after the expiry date printed on the pack.